1. Field of the Invention
The present invention relates to a probe assembly of an infrared thermometer and more particularly to a probe assembly capable of detecting the surface temperature of a thermal radiation source and suitable for holding over human skin or inserting into a patient's ear canal for accurately taking human body temperature.
2. Description of the Related Art
The infrared thermometer is a kind of non-contact temperature measurement apparatus. It is adapted to aim at the preferred surface of an unmeasured object such as a machine, a household appliance, a heated material and a mammal, and the detected temperature can be read after a short period (even less than one second). All objects give off heat and emit thermal radiation. The wavelength of the thermal radiation generally ranges between three and fourteen micrometers. In optics, such thermal radiation rays are called infrared rays. The measuring principle of the infrared thermometer is to detect the radiation flux or the wavelength of the received infrared rays so as to figure out the object's temperature.
Especially during medical diagnosis, a clinical thermometer is very helpful to doctors. In comparison with the oral cavity, the anus or the armpit, the eardrum is known to have a temperature very near to that of the body's core temperature. The infrared thermometer can detect radiant heat of the infrared rays emitting from the eardrum through insertion into patient's ear canal so as to determine the temperature of the eardrum. Therefore, the infrared thermometer is becoming more and more popular, and shows great promise as an effective means for accurately measuring and displaying patient's eardrum temperatures very rapidly, typically within two seconds. In this regard, hospitals, clinics and families also replace conventional mercury thermometers with the infrared thermometers. However, the infrared thermometer probe for insertion into a patient's ear canal still contacts the patient's skin during measurement so that the probe is likely to be contaminated by the patient's secretions. Accordingly, the infrared thermometer is modified to be suitable for measuring the patient's forehead temperature. No matter what part of the patient or thermal radiation source is for measurement, the design principles of the infrared thermometers hardly vary.
Unfortunately, the infrared thermometer probe available on the medical market has either a large volume or an inaccurate measurement resulting from inadequate temperature transformation. For example, U.S. Pat. No. 4,895,164 entitled “Infrared Clinical Thermometer” discloses a probe assembly with a waveguide and an infrared detector being held in an isothermal state at ambient temperature by a heat-conducting block. The drawback of this approach is that a substantially large heat-conducting block is required so that the thermometer has a large volume unfavorable for handy use. In addition, an isothermal condition is not necessary in the design of a probe assembly. Since the surfaces of most waveguides are coated with a layer of gold, which has very high reflectivity and very low emissivity (around 10%), even though a temperature difference exists between the infrared detector and the waveguide, the infrared detector assembly receives little thermal radiation emitted from the inner wall of the waveguide. Furthermore, the property of the gold layer on the waveguide varies during a durable use period or between coating process parameters. Such uncertainty lessens the accuracy of the temperature measurement.
Instead of the aforesaid probe with the waveguide, U.S. Pat. No. 5,018,872 discloses a probe assembly 10 of another kind, as shown in FIG. 1. A transparent cover 11 is stretched over a whole trumpet-like plastic tube 17. A cylindrical shield 13 is inside the plastic tube 17 and adjacent to the left open end 19 of the plastic tube 17. An infrared radiation sensor 15 is located within the elongated portion of the plastic tube 17, and its base is against the end of a metallic heat sink 14. Therefore, the heat sink 14 can rapidly takes the heat accumulated on the infrared radiation sensor 15 from the tube's exterior so that the cold junction of the thermopile chip in the infrared radiation sensor 15 can be kept at a constant temperature.
However, it is necessary for the heat sink 14 to have a sufficiently large volume so as to rapidly conduct the heat from the cylindrical shield 13 and the plastic tube 17 to itself. Consequently, the infrared thermometer is too heavy to be handily held. On the other hand, because the heat sink 14, infrared radiation sensor 15 and plastic tube 17 are tightly combined with each other, the heat is easily and directly transferred through junctions between them. If the heat sink 14 does not have a sufficient volume, the temperature of the aforesaid cold junction is likely to have an immediate fluctuation. That is, the accuracy of the measured temperature is lessened. Since the heat sink 14 and infrared radiation sensor 15 directly contact each other through a large-area interface, external heat is absorbed by the heat sink 14 and cannot rapidly be conducted to the whole interior of the heat sink 14 so that the infrared radiation sensor 15 is also heated through the interface.
Referring to U.S. Pat. No. 6,292,685 (Pompei), Pompei discloses an infrared thermometer adapted to detect the temperature of a patient's forehead. Furthermore, the heat sink of the infrared thermometer is press fit in a plastic cap which is threaded on to a tubular head. Even though the infrared radiation sensor is separated from the heat sink by a ring, the heat sink directly heated by the plastic cap can cause the can thermal unbalance through thermal convection and thermal radiation after the plastic cap contacts patient's warm body or a heat source.
In conclusion, the medical market urgently requires a light and stable probe assembly so as to enable the infrared thermometer to be handily used and immediately display an accurate measured temperature.